Blue light increases thermal bleaching tolerance of coral via remodeling host-Symbiodiniaceae symbiosis

Given the high degree of heterogeneity of coral bleaching, there is potential for abiotic approaches to improve the thermal tolerance of coral. However, there is limited knowledge about such factors and causes that regulating acclimation of coral to warming. Here, a study was conducted on the reef building coral Acropora tenuis to investigate the impact of light qualities on the physiological, cellular, and molecular biochemical responses of the coral holobiont to heat stress. The results showed that after subjecting the samples to heat stress at 32 celcius for 9 days, over 90% corals exposed to compound light experienced bleaching on the fifth day, while corals exposed to blue light showed no significant signs of bleaching even on the ninth day. This indicates that blue light may enhanced the coral's thermal bleaching tolerance. Further analysis revealed blue light primarily increased coral's resistance to thermal bleaching by remodeling the interactions between Symbiodiniaceae (i.e. decreased photosynthesis, respiration and ROS release) and coral (i.e. decreased respiration and lipid peroxidation). The study also found that the host's of reactive oxygen species (ROS) played a role in causing coral bleaching besides the ROS released by Symbiodiniaceae. The up-regulation of the DAO gene (encoding D-amino-acid oxidase, upregulated nearly 1000 times under warming conditions) in the host highlights the mechanism of coral bleaching, whereby the catalysis of amino acids by the D-amino-acid oxidase produces ROS. In summary, the present study reveals novelty insights into the molecular processes related to thermal bleaching of coral, identifies blue light as a positive environmental factor that enhances coral's tolerance to global warming.